1. Field of the Invention
The invention relates to annular flanges for fastening rotor or stator elements in a turbine, and also to a turbomachine including such a turbine.
2. Description of the Related Art
In a turbomachine the rotor disks (e.g. turbine disks) are connected together by annular flanges at their radially inner peripheries, those flanges pressing against one another and being fastened together by bolting.
Other elements, such as annular supports for labyrinth seals, may also include annular flanges at their inner peripheries, which flanges are clamped between two annular rotor disk flanges and fastened by the same bolts as the rotor disks.
Such annular flanges are generally festooned, i.e. they have alternating solid portions and hollow portions so as to reduce their weight. The holes for passing the fastener bolts are formed through the solid portions.
In order to fasten together a plurality of juxtaposed flanges, it is necessary for all of the holes formed through the solid portions of the flange to be in alignment so as to avoid the hollow portions of one of the flanges being angularly offset so as to be in alignment with the bolt-passing holes formed in the solid portions of other flanges, which would lead to that flange being clamped between two other flanges without being fastened to the other flanges.
In the Applicants' application FR 08/02918, proposals are made for at least one bottom of a hollow portion in the inner periphery to be situated radially inside a circle centered on the axis of the flange and to be externally tangential to the orifices in the solid portions. Thus, in the event of a flange being angularly offset in such a manner that its orifices are not in alignment with the orifices in the other flanges, then the bottom of at least one of the hollow portions of said flange is situated on the path of at least one fastener bolt and prevents it from being inserted through the orifices of the other flanges, thereby avoiding any risk of the flange being wrongly assembled.
It has been found that such a hollow portion performing a keying function gives rise to a modification to the tangential stress lines in the flange, thereby leading to an increase in stress concentration in the solid portions adjacent to the keying hollow portion. Those stresses are at a maximum in those zones of the solid portions adjacent to the keying hollow portion that are connected to the following hollow portions. It is also observed that stresses are increased in the orifices of the solid portions adjacent to the keying hollow portion.
Such an increase in local stress concentration may lead to the formation of cracks in the zones where stresses are concentrated, thereby limiting the lifetime of the festooned flange.